I used homemade Italian meringue buttercream frosting for the filling in these cookies. I couldn’t find the exact recipe, but this one is pretty close!
I highly recommend doubling the recipe because I always run out and the frosting will last for a few weeks in the refrigerator.
A final note on the baking instructions: I cut out my cookies with a standard-sized shot glass, and baked them at 400 degrees for 5 minutes. You have to really watch these cookies because the bottom browns quickly. Remove them from the oven when the top of the cookies are puffed up, but the bottoms are still white. Place them immediately on a cool surface so the pan does not continue to cook the cookies. In this case, pale is better!